1. Technical Field
This invention relates to imaging media suitable for use with ink-jet printers. More particularly, the invention relates to ink-jet recording media comprising a paper substrate coated on one surface with a radiation-curable composition and an ink-receptive composition. The other surface of the paper may be coated with a polymeric coating to improve the paper""s dimensional stability. The invention also encompasses a continuous in-line process for making such imaging media.
2. Brief Description of the Related Art
Today, individual consumers and businesses are turning to ink-jet printing systems and digital technology to produce many different imaging media products. With the introduction of new computers, software, and digital cameras, consumers are now able to create greeting cards, posters, calendars, newsletters, fliers, window decals and the like in the comfort of their own homes. Companies can create small format products such as business cards, company newsletters, brochures, promotional materials, overhead transparencies, and the like. Companies can also create large indoor and outdoor advertising displays and other graphic art materials for business presentations.
In an ink-jet printing process, liquid ink is squirted through very fine nozzles in a printer. The resultant ink droplets form an image directly on a recording medium that typically comprises a coated film or paper substrate. The quality of the final image or text is partly dependent on the composition of the ink-jet recording medium particularly the coating(s) and substrate. The inks used in most ink-jet printers are aqueous-based inks containing molecular dyes or pigmented colorants. Water is the major component in aqueous-based inks. Small amounts of water-miscible solvents such as glycols and glycol ethers also may be present. Other ink-jet inks are non-aqueous based inks containing organic vehicles (e.g., hydrocarbon solvents) as the major component.
xe2x80x9cPhoto-papersxe2x80x9d are particularly popular, because a person can produce photographic-like images on these materials. Paper substrates, e.g., plain papers, clay-coated papers, and polyethylene resin-coated papers, can be used to make photo papers. The paper substrate is coated with specially formulated coatings that are capable of receiving aqueous-based inks from ink-jet printers.
Often, the substrate is a polyethylene-coated paper. Such papers can have good dimensional stability and moisture resistance. The polyethylene coating acts as a moisture-barrier layer helping to prevent the aqueous ink vehicle from permeating into the base paper. Polyethylene-coated papers are commercially available from Jen-Coat, Inc. (Westfield, Mass.) and other companies under various trademarks. However, there are some disadvantages with using polyethylene-coated papers, including their manufacturing costs and thermal stability. For example, it may be difficult to use polyethylene-coated papers in high temperature manufacturing operations, such as those where additional coating layers must be dried, because of polyethylene""s thermoplastic properties. Further, some polyethylene-coated papers tend to have low surface gloss which may be undesirable for some commercial applications. As an alternative, clay-coated papers can be used. The cost of clay-coated papers is generally lower. But, clay-coated papers tend to absorb the aqueous ink vehicle and this absorption may lead to curling of the paper""s edges and cockling of the paper""s surface.
D""Anna et al., U.S. Pat. No. 5,800,884 discloses a gloss coating composition comprising radiation curable oligomers and monomers, and photosensitizers. The coating composition is applied to at least one surface of a substrate and exposed to an ultraviolet light source resulting in curing of the composition onto the substrate""s surface. The patent discloses that the coating can be applied to non-woven, woven, synthetic paper, paper, paperboard, plastic, or metal substrates. The patent further discloses that the coating composition can be used as primer coat over a substrate""s surface, wherein the coating surface is capable of printing with ultraviolet or ultraviolet compatible inks. Alternatively, or in addition, to the primer coat, the coating compositions are used as a top coat over a substrate surface to impart gloss characteristics, good rub resistance, and flexibility to the substrate.
Nowak, U.S. Pat. No. 4,265,976 discloses an ultraviolet radiation-curable coating composition comprising (1) chlorinated rubber, (2) chlorinated paraffin, (3) vinyl acetate, (4) trimethylolpropane triacrylate, (5) photoinitiator, and (6) heat and light stabilizers for the chlorocarbon components. The patent discloses that the coating has utility as a moisture-barrier film for the protection of substrates such as paper and cardboard. For example, the patent discloses the coating system can provide a moisture-barrier coating on detergent boxes in a single coat procedure.
Mehta et al., U.S. Pat. No. 5,219,641 discloses using a radiation-curable coating on certain substrates to make them receptive to images from a thermal transfer printer. The coating is a blend of radiation-curable oligomers and monomers, and optionally a free radical initiator. The patent discloses that the coating may be applied to coated or non-coated electronic data processing papers, bond papers, high quality calendared papers, cast coated papers, and other business forms.
The ink-jet industry is looking to develop new paper-based media capable of absorbing aqueous inks to form high quality images having good color density, brilliance, and resolution. The media should have good moisture-barrier properties and preferably have high surface gloss. A cost-effective and efficient manufacturing process for making such media would also be desirable. The present invention provides such ink-jet recording media and a continuous in-line process for manufacturing the media.
The ink-jet recording media of this invention comprise a radiation-cured layer and polymeric ink-receptive layer. The radiation-cured layer helps retain the surface gloss of the media and provides good moisture barrier properties. Significantly, the radiation-cured layer is thermally stable at temperatures greater than temperatures at which conventional polyethylene and related thermoplastic materials (e.g., olefin-based polymers and copolymers) are thermally stable.
The present invention relates to an ink-jet recording medium comprising: a) a paper substrate, b) a radiation-cured layer overlaying a surface of the paper substrate, and c) a polymeric ink-receptive layer overlaying the radiation-cured layer, the ink-jet recording medium having a water vapor transmission rate of no greater than 12 grams per 100 square inches per 24 hours (5 g/100 in2/24 hrs). Preferably, the water vapor transmission rate is no greater than 8 g/100 in2/24 hrs. The medium preferably has a glossy surface luster. In such glossy media embodiments, the surface gloss is at least 70, and it is more preferably in the range of about 85 to about 95. In other embodiments, satin-like media having surface gloss values in the range of 20 to 70 can be made. In still other embodiments, matte-like media having surface gloss values less than 20 can be made.
Preferably, the paper substrate is a clay-coated paper having a thickness in the range of about 4 to about 8 mils. The radiation-cured layer can be formed by irradiating a coating comprising a radiation-curable oligomer and photoinitiator. Preferably, the coating used to form the radiation-cured layer comprises at least about 60% oligomer and 3% photoinitiator by weight. The coating can further comprise radiation-curable monomer and additives. For example, a coating comprising 60% oligomer, 3% photoinitiator, 20% monomer, 15% pigment, and 2% UV light stabilizer by weight can be used. Suitable oligomers include acrylated polyethers, acrylated polyesters, and acrylated acrylics. Suitable monomers include trimethylolpropane trimethacrylate. Suitable photoinitiators include 1-hydroxy-cyclohexyl phenyl ketone and a blend of trimethylbenzophenone, polymeric hydroxy ketone, and trimethylbenzoyldiphenyl phosphine oxide. Generally, the radiation-cured layer has a weight in the range of about 1 to about 40 grams/square meter. Ultraviolet light or electron beam irradiation can be used to cure the coating.
The ink-receptive layer can comprise a water-soluble binder resin, for example, polyvinyl alcohols, poly(vinyl pyrrolidone), poly(2-ethyl-2-oxazoline), methylcellulose, poly(ethylene oxide), and copolymers and mixtures thereof. Preferably, the coating comprises at least 40% water-soluble binder by weight. The coating can further comprise a water-dispersible resin. Multiple ink-receptive layers can be applied to substrate. Generally, the dry coat weight of the ink-receptive layer is in the range of about 5 to about 50 grams/square meter.
In another embodiment of this invention, the back surface of the base paper is coated with a polymeric coating that further helps prevent moisture from penetrating into the base paper. Suitable water-dispersible resins include, for example, polyvinyl chloride; vinyl chloride copolymers; polyvinylidene chloride; vinylidene chloride copolymers; acrylates; methacrylates; polyvinyl acetate; polyacrylonitrile; polystyrene; styrene copolymers; and mixtures thereof. Alternatively, the polymeric layer on the back surface of the paper can be a radiation-cured layer formed by irradiating a coating containing radiation-curable oligomers, monomers, photoinitiators and additives.
The present invention also relates to a continuous in-line process for making an ink-jet recording medium. In one embodiment, the process comprises the steps of a) applying a radiation-curable coating to a surface of a substrate material, b) irradiating the radiation-curable coating so that the coating undergoes a curing process, and c) applying an ink-receptive coating over the irradiated coating. Preferably, the media produced by the continuous process have a water vapor transmission rate of no greater than 12 g/100 in2/24 hrs and more preferably no greater than 5 g/100 in2/24 hrs. Glossy media having a surface gloss greater than 70 as well as satin-like media having a surface gloss in the range of 20 to 70 and matte-like media having a surface gloss less than 20 can be made. The irradiated coating can be treated with corona discharge prior to applying the ink-receptive coating. In another embodiment, a coating comprising adhesion promoters can be applied over the irradiated coating prior to application of the ink-receptive coating. As described above, the back surface of the substrate material can be coated with a polymeric coating to enhance the material""s dimensional stability. The continuous in-line process can run at a speed of at least about 60 feet per minute. The irradiated coating has good thermal stability. Thus, the substrate comprising the irradiated coating can be subjected to further treatments and processing at temperatures (e.g., 140xc2x0 C. to 200xc2x0 C.) greater than temperatures at which conventional polyethylene and related thermoplastic materials (e.g., olefin-based polymers and copolymers) are typically treated and processed.